MK 108
| MK 108 | |
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| general information | |
| Military designation: | MK 108 |
| Country of operation: | German Empire |
| Developer / Manufacturer: | Rheinmetall |
| Manufacturer country: | German Empire |
| Weapon Category: | Automatic cannon |
| Technical specifications | |
| Caliber : | 30 × 90 RB |
| Cadence : | 650 rounds / min |
| Charging principle: | Recoil loader |
| Lists on the subject | |
The machine cannon MK 108 from Rheinmetall-Borsig was a heavy on-board weapon in 30 mm caliber for German fighter planes at the time of the Second World War .
history
The development of the MK 108 began in 1940 without a government contract from the Rheinmetall -Borsig company. The weapon was intended as a heavy on-board weapon for German fighters. After a demonstration of the prototype, Colonel General Ernst Udet, who was then General Luftzeugmeister, refused any further development . It was only after the death of Udet in 1941 and the demand for a more powerful weapon on the part of the fighter pilots that the MK 108 was further developed. The need for a heavy on-board weapon with a caliber of 30 mm also became more urgent because the size of the weapon became more urgent during the war of enemy bombers and their bullet resistance increased due to the reinforced armor. Furthermore, the strong defensive fire of the enemy bombers operating in closed groups and the escorting escort fighters (for example North American P-51 ) forced the German fighters to carry out their attacks at the highest possible speed. The heavy bombers, as preferred targets, were only in effective range for a very short moment and could only be fired at for a short time. It therefore became all the more important to increase the number of projectiles and also to increase their destructive power. Accordingly, the MK 108 was specially developed to combat relatively slow-flying bomb-carrying combat aircraft.
The MK 108 was a compact weapon with a comparatively low weight and a high rate of fire. The problems of the MK 103 in terms of weight and length - the MK 108 was 88 kg lighter and 1260 mm shorter - were reduced and the rate of fire increased to around 650 rounds per minute. However, this was done at the expense of a significantly lower muzzle velocity. The MK 108 also tended to jam due to the increased G-load that occurs during cornering battles. Thanks to its compact dimensions, the MK 108 could also be installed comparatively easily in single-engine hunting machines, where it replaced the MG 151/20 as a motor cannon in the / U4 versions of the Bf 109G . The R2 upgrade kit was used in the outer wing of the Focke-Wulf Fw 190-A-7 / A-8 used to fight bombers; these aircraft were also used as storm fighters .
The first MK 108s were built into the Bf 109 G-6 / U4 in June 1943 as motor cannons and were used by the German Air Force until the end of the war in 1945, including armament for the Messerschmitt Me 262 . In terms of caliber 30 mm, it was the standard cannon of the Luftwaffe until the end of the war .
The cartridge weight was 480 g, the bullet weight 330 g. Mainly mine projectiles were fired.
Work was carried out on the successor model MK 112 until 1945 , which however only achieved prototype status.
function
The MK 108 is an open firing weapon. This means that there is no cartridge in the chamber before the shot and the slide is at the back. The gun is open before the trigger. As a result, there is no cartridge in the hot-shot tube when it is ready to fire, which greatly reduces the risk of self-ignition and allows the tube to be cooled by air flow.
In contrast to the MK 103, the MK 108 does not have a locking mechanism. It is a pure spring-mass lock . To keep the mass of the breech acceptably low, the barrel length had to be kept short (and thus the muzzle velocity low). In the design of the MK 108, the emphasis was on simple construction, high bullet weight and high rate of fire, but at the expense of the muzzle velocity.
In order to finish loading the weapon (ready to fire), it must be pneumatically reloaded. The closure is pulled back from the loading piston using compressed air and the closing springs are tensioned. After releasing the charging button, the electropneumatic charging valve closes and the charging piston is brought into its starting position by a compression spring, while the bolt is caught in the cocked position by the trigger. The cartridge belt was advanced by half a belt division via the control cams of the lock and the control lever of the belt feed.
After pressing the trigger, an electromagnetic switch (the so-called firing contactor) responds. This gives the electro-pneumatic trigger valve and the ignition converter power. The opening trigger valve lets compressed air flow to the trigger device. The piston of the trigger device, charged with compressed air, controls the trigger bolt downwards. This releases the lock, which is under the pressure of the tensioned closing springs, and snaps forward. On the way forward, the lock actuates the belt feed. The cartridge belt is transported by the belt slider by half a belt division so that a cartridge is brought into the feed position and pushed out of the cartridge belt by the lock. This cartridge is pushed into the barrel chamber by the advancing bolt. Before the front end position of the lock is reached, the extractor claw is placed in the extractor groove of the cartridge case and the cartridge is ignited electrically. The ignition circuit is closed when the locking contact spring hits the ignition rail in the weapon housing. Electric current flows through the ignition pin through a very thin wire in the cartridge's primer. The wire is heated strongly, burns up in a very short time and ignites the ignition charge. The propellant powder in the cartridge is ignited via the primer and the shot is broken. After the ignition wire burns up, the ignition circuit is interrupted immediately.
Even before it reaches its front end position, the bolt is accelerated backwards by the recoil impulse and the closing springs are tensioned. The fired cartridge case is pulled out of the cartridge chamber by the extractor claw and - a special feature of the MK 108 - is not ejected, but rather pulled into the empty pocket of the cartridge belt. After passing through, the belt breaks up into the individual links with the cartridge cases.
After the extractor claw has released the retracted cartridge case, the slide continues to move backwards until it reverses. The return energy of the lock is consumed by two closing and two ring springs.
As long as the trigger device is pressurized with compressed air, the shutter can advance unhindered and feed and ignite cartridges ( continuous fire ). If the trigger valve is de-energized, the trigger piston is depressurized and returns to its starting position. This releases the trigger bar and lifts it up through strong compression springs. The trigger bar enters the slide and catches the advancing slide. The fire is interrupted.
Through-loading device and discharge device are locked against each other. This prevents simultaneous loading and unloading.
Technical specifications
- Type: single barrel machine gun
- Function: recoil loader
- Caliber: 30 × 90 RB
- Manufacturer: Rheinmetall-Borsig
- Length: 1057 mm
- Tube length 545 mm
- Weight: 58 kg
- Rate of fire (per min): 650
- Muzzle velocity: 505-540 m / s
- Projectile weight: 330 g
- Cartridge weight: 480 g
- Muzzle energy: 42,079-48,114 joules
Trivia
The weapon was referred to as a jackhammer in soldiers' jargon because of the rate of fire .
literature
- Hanfried Schliephake: Aircraft Armament - The Air Force's on-board weapons from the beginning to the present. Motorbuch Verlag, Stuttgart 1977, ISBN 3-87943-486-7 , p. 157ff.
- Manfred Griehl: German aircraft armament until 1945. Motorbuch Verlag, Stuttgart 2008, ISBN 978-3-613-02849-4 , p. 29f.
Web links
- Rheinmetall Borsig Mk108 on stormbirds.com (English)
- Effect of a three-shot volley from an MK 108 on the wing of a Spitfire (photo from a test site)
Individual evidence
- ↑ after Griehl: German aircraft armament . P. 29; Schliephake: Aircraft armament . P. 157.
- ↑ Hanfried Schliephake: Aircraft Armament - The Air Force's on-board weapons from the beginning to the present. P. 161.
- ^ Anthony G. Williams: Rapid Fire. ISBN 1-84037-122-6 , p. 67.
- ↑ Achim Schnurrer: Bachem "Natter" secret project: Hell ride on the wooden rocket. In: Spiegel Online . March 1, 2010, accessed June 9, 2018 .